U.S. patent application number 12/780455 was filed with the patent office on 2010-12-16 for multi-cell processing architectures for modeling and impairment compensation in multi-input multi-output systems.
Invention is credited to Seyed Aidin BASSAM, Fadhel M. Ghannouchi, Mohamed Helaoui.
Application Number | 20100316157 12/780455 |
Document ID | / |
Family ID | 43123509 |
Filed Date | 2010-12-16 |
United States Patent
Application |
20100316157 |
Kind Code |
A1 |
BASSAM; Seyed Aidin ; et
al. |
December 16, 2010 |
MULTI-CELL PROCESSING ARCHITECTURES FOR MODELING AND IMPAIRMENT
COMPENSATION IN MULTI-INPUT MULTI-OUTPUT SYSTEMS
Abstract
The present invention relates to a method for multiple-input
multiple-output impairment pre-compensation comprising: receiving a
multiple-input signal; generating a pre-distorted multiple-input
signal from the received multiple-input signal; generating a
multiple-output signal by feeding the pre-distorted multiple-input
signal into a multiple-input and multiple-output transmitter;
estimating impairments generated by the multiple-input and
multiple-output transmitter; and adjusting the pre-distorted
multiple-input signal to compensate for the estimated impairments.
The present invention also relates to a pre-compensator for use
with a multiple-input and multiple-output transmitter, comprising:
a multiple-input for receiving a multiple-input signal; a matrix of
pre-processing cells for generating a pre-distorted multiple-input
signal from the received multiple-input signal; and a
multiple-output for feeding the pre-distorted multiple-input signal
to the multiple-input and multiple-output transmitter. The
pre-processing cells are configured so as to estimate impairments
generated by the multiple-input and multiple-output transmitter and
adjust the pre-distorted multiple-input signal to compensate for
the estimated impairments.
Inventors: |
BASSAM; Seyed Aidin;
(Calgary, CA) ; Ghannouchi; Fadhel M.; (Calgary,
CA) ; Helaoui; Mohamed; (Calgary, CA) |
Correspondence
Address: |
DOWELL & DOWELL P.C.
103 Oronoco St., Suite 220
Alexandria
VA
22314
US
|
Family ID: |
43123509 |
Appl. No.: |
12/780455 |
Filed: |
May 14, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61213176 |
May 14, 2009 |
|
|
|
Current U.S.
Class: |
375/267 |
Current CPC
Class: |
H04B 7/0632 20130101;
H04B 7/0639 20130101; H04L 25/03343 20130101; H04B 7/0456 20130101;
H04B 1/0475 20130101; H04L 25/03891 20130101; H04B 7/0417
20130101 |
Class at
Publication: |
375/267 |
International
Class: |
H04L 27/28 20060101
H04L027/28 |
Claims
1. A method for multiple-input multiple-output impairment
pre-compensation comprising: receiving a multiple-input signal;
generating a pre-distorted multiple-input signal from the received
multiple-input signal; generating a multiple-output signal by
feeding the pre-distorted multiple-input signal into a
multiple-input and multiple-output transmitter; estimating
impairments generated by the multiple-input and multiple-output
transmitter; and adjusting the pre-distorted multiple-input signal
to compensate for the estimated impairments.
2. The method of claim 1, wherein generating a pre-distorted
multiple-input signal comprises feeding the received multiple-input
signal to a matrix of pre-processing cells.
3. The method of claim 1, wherein adjusting the pre-distorted
multiple-input signal includes introducing linear and nonlinear
distortions on each signal path of the multiple-input signal.
4. The method of claim 3, wherein adjusting the pre-distorted
multiple-input signal further includes introducing interference
between each signal path of the multiple-input signal.
5. The method of claim 2, wherein each of the pre-processing cells
includes nonlinear processing blocks compensating for
multiple-input multiple-output nonlinear distortions and an effect
of interferences between signal paths of the multiple-input, signal
and signal paths of the multiple-output signal.
6. The method of claim 5, comprising, in the nonlinear processing
blocks: processing the multiple-input signal and the
multiple-output signal to determine a desired multiple-output
signal that pre-compensates for the nonlinear distortions; and
estimating a nonlinear function for each nonlinear processing
block.
7. The method of claim 2, wherein each of the pre-processing cells
includes linear processing blocks compensating for multiple-input
multiple-output linear distortions and an effect of interferences
between signal paths of the multiple-input signal and signal paths
of the multiple-output signal.
8. The method of claim 7, comprising, in the linear processing
blocks: processing the multiple-input signal and the
multiple-output signal to determine a desired multiple-output
signal that pre-compensates for the linear distortions; and
estimating a linear function for each linear processing block.
9. The method of claim 2, comprising, in each of the pre-processing
cells of the matrix: nonlinear processing blocks compensating for
multiple-input multiple-output nonlinear distortions and an effect
of interferences between signal paths of the multiple-input signal
and signal paths of the multiple-output signal; and linear
processing blocks compensating for the multiple-input
multiple-output linear distortions and the effect of interferences
between the signal paths of the multiple-input signal and the
signal paths of the multiple-output signal.
10. The method of claim 9, comprising, in the non-linear and linear
processing blocks: processing the multiple-input signal and the
multiple-output signal to determine a desired multiple-output
signal that pre-compensates for the non-linear and linear
distortions; estimating a non-linear function for each non-linear
processing block; and estimating a linear function for each linear
processing block.
11. The method of claim 2, wherein each of the pre-processing cells
of the matrix models a behavior of multi-input multi-output
system.
12. The method of claim 11, wherein each of the pre-processing
cells of the matrix include: a nonlinear processing block to
compensate for the multiple-input multiple-output system linear
distortions and an effect of interferences between signal paths of
the multiple-input signal and signal paths of the multiple-output
signal; and a linear processing block to compensate for the
multiple-input multiple-output system linear distortions and the
effect of interferences between the signal paths of the
multiple-input signal and the signal paths of the multiple-output
signal.
13. The method of claim 12, comprising, in each of the non-linear
and linear processing blocks: processing the multiple-input signal
and the multiple-output signal to determine a desired
multiple-output signal that pre-compensates for the non-linear and
linear distortions; estimating a non-linear model for each
non-linear processing block; and estimating a linear model for each
linear processing block.
14. A pre-compensator for use with a multiple-input and
multiple-output transmitter, comprising: a multiple-input for
receiving a multiple-input signal; a matrix of pre-processing cells
for generating a pre-distorted multiple-input signal from the
received multiple-input signal; and a multiple-output for feeding
the pre-distorted multiple-input signal to the multiple-input and
multiple-output transmitter; wherein the pre-processing cells are
configured so as to estimate impairments generated by the
multiple-input and multiple-output transmitter and adjust the
pre-distorted multiple-input signal to compensate for the estimated
impairments.
15. The pre-compensator of claim 14, wherein the adjustment of the
pre-distorted multiple-input signal introduces linear and nonlinear
distortions on each signal path of the multiple-input signal.
16. The pre-compensator of claim 15, wherein the adjustment of the
pre-distorted multiple-input signal further introduces interference
between each signal path of the multiple-input signal.
17. The pre-compensator of claim 14, wherein each of the
pre-processing cells includes nonlinear processing blocks
compensating for multiple-input multiple-output nonlinear
distortions and an effect of interferences between signal paths of
the multiple-input signal and signal paths of the multiple-output
signal.
18. The pre-compensator of claim 17, wherein the nonlinear
processing blocks are configured so as to: process the
multiple-input signal and the multiple-output signal to determine a
desired multiple-output signal that pre-compensates for the
nonlinear distortions; and estimate a nonlinear function for each
nonlinear processing block.
19. The pre-compensator of claim 14, wherein each of the
pre-processing cells includes linear processing blocks compensating
for multiple-input multiple-output linear distortions and an effect
of interferences between signal paths of the multiple-input signal
and signal paths of the multiple-output signal.
20. The pre-compensator of claim 19, wherein the linear processing
blocks are configured so as to: process the multiple-input signal
and the multiple-output signal to determine a desired
multiple-output signal that pre-compensates for the linear
distortions; and estimate a linear function for each linear
processing block.
21. The pre-compensator of claim 14, wherein each of the
pre-processing cells of the matrix includes: nonlinear processing
blocks compensating for multiple-input multiple-output nonlinear
distortions and an effect of interferences between signal paths of
the multiple-input signal and signal paths of the multiple-output
signal; and linear processing blocks compensating for
multiple-input multiple-output linear distortions and the effect of
interferences between the signal paths of the multiple-input signal
and the signal paths of the multiple-output signal.
22. The pre-compensator of claim 21, wherein the non-linear and
linear processing blocks are configured so as to: process the
multiple-input signal and the multiple-output signal to determine a
desired multiple-output signal that pre-compensates for the
non-linear and linear distortions, respectively; for the non-linear
processing blocks, estimate a non-linear function for each
non-linear processing block; and for the linear processing blocks,
estimate a linear function for each linear processing block.
23. The pre-compensator of claim 14, wherein each of the
pre-processing cells of the matrix models the behavior of a
multi-input multi-output system.
24. The pre-compensator of claim 22, wherein each of the
pre-processing cells of the matrix include: a nonlinear processing
block to compensate for multiple-input multiple-output system
linear distortions and an effect of interferences between signal
paths of the multiple-input signal and signal paths of the
multiple-output signal; and a linear processing block to compensate
for multiple-input multiple-output system linear distortions and
the effect of interferences between the signal paths of the
multiple-input signal and the signal paths of the multiple-output
signal.
25. The pre-compensator of claim 24, wherein each of the non-linear
and linear processing blocks is configured so as to: process the
multiple-input signal and the multiple-output signal to determine a
desired multiple-output signal that pre-compensates for the
non-linear and linear distortions; for the non-linear processing
blocks, estimate a non-linear model for each non-linear processing
block; and for the linear processing blocks, estimate a linear
model for each linear processing block.
26. A compensator for use with a multiple-input and multiple-output
transmitter, comprising: a multiple-input for receiving a
multiple-input signal; a matrix of processing cells for generating
a distorted multiple-input signal from the received multiple-input
signal; and a multiple-output for feeding the pre-distorted
multiple-input signal; wherein the pre-processing cells are
configured so as to estimate impairments generated by the
multiple-input and multiple-output transmitter and adjust the
pre-distorted multiple-input signal to compensate for the estimated
impairments.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefits of U.S. provisional
patent application No. 61/213,176 filed on May 14, 2009, which is
herein incorporated by reference.
TECHNICAL FIELD
[0002] This present disclosure relates to the field of wireless
communications, and more specifically, to the distortions and
impairment's corrections of Multiple Input Multiple Output (MIMO)
systems with linear and nonlinear components and unwanted
interactions and correlations between multiple input signals.
BACKGROUND
[0003] MIMO refers to a system with multiple inputs and multiple
outputs. The definition of MIMO system is extended to wireless
communication topologies in which multiple modulated signals,
separated in frequency or space domain, are simultaneously
transmitted through a single/multiple branch radiofrequency (RF)
front-end.
[0004] MIMO systems, with modulated signals separated in space
domain, refer to wireless topologies with multiple branches of RF
front-ends, with all branches simultaneously involved in signal
transmission. These types of MIMO systems are considered as
Multi-branch MIMO systems.
[0005] MIMO systems, with modulated signals separated in frequency
domain, refer to systems where multiple signals modulated in
different carrier frequencies are concurrently transmitted through
a single branch RF front-end. These types of MIMO systems are
considered as Multi-frequency MIMO systems. Examples of
multi-frequency MIMO systems are concurrent dual-band and
multi-carrier transmitters. The system in frequency domain
comprises two independent baseband signals as the multiple inputs
and two up-converted and amplified signals at two carrier
frequencies as the multiple outputs. In fact, this type of MIMO
system uses a single branch RF front-end to transmit multiple
signals.
[0006] RF MIMO systems are composed of linear and nonlinear
components and/or sub-blocks which may results in signal quality
degradation. For example, the power amplifier (PA) is one of the
main building blocks of the RF front-end that has a significant
nonlinear behavior. This nonlinear relation between the input
signal and the amplified output signal of the transmitter results
in significant distortions on the output signal. These distortions
significantly degrade the output signal's quality and result in
poor data communications. In this regard, different techniques to
compensate for these distortions were proposed in order to improve
the linearity of the RF radio front-end.
[0007] Also, there are unwanted and unavoidable interactions and
correlations between the different signals in a MIMO system. These
interactions are combined with the linear and nonlinear distortions
in each branch of the MIMO system to generate more complex
distortion effects, which considerably degrade the performance of
the MIMO system. The effect of these complex distortions cannot be
eliminated or reduced with conventional signal processing
algorithms applied to Single Input Single Output (SISO)
systems.
[0008] Therefore, there is a need for a signal processing technique
for MIMO systems that compensates for any distortion, interactions,
and crosstalk in the system in order to improve the signal quality
of the transmission link.
SUMMARY
[0009] MIMO systems require special processing architectures, which
compensate for the complex distortions in order to transmit and/or
receive good quality signals. Processing architectures that are
conventionally used with SISO system do not consider the
interactions between the different input signals of the MIMO
systems. This requires a more complex processing architecture that
considers the effect of interaction between the multiple input
signals.
[0010] Therefore, according to the present invention, there is
provided a method for multiple-input multiple-output impairment
pre-compensation comprising: receiving a multiple-input signal;
generating a pre-distorted multiple-input signal from the received
multiple-input signal; generating a multiple-output signal by
feeding the pre-distorted multiple-input signal into a
multiple-input and multiple-output transmitter; estimating
impairments generated by the multiple-input and multiple-output
transmitter; and adjusting the pre-distorted multiple-input signal
to compensate for the estimated impairments.
[0011] According to the present invention, there is also provided a
pre-compensator for use with a multiple-input and multiple-output
transmitter, comprising: a multiple-input for receiving a
multiple-input signal; a matrix of pre-processing cells for
generating a pre-distorted multiple-input signal from the received
multiple-input signal; and a multiple-output for feeding the
pre-distorted multiple-input signal to the multiple-input and
multiple-output transmitter; wherein the pre-processing cells are
configured so as to estimate impairments generated by the
multiple-input and multiple-output transmitter and adjust the
pre-distorted multiple-input signal to compensate for the estimated
impairments.
[0012] The present invention further relates to a compensator for
use with a multiple-input and multiple-output transmitter,
comprising: a multiple-input for receiving a multiple-input signal;
a matrix of processing cells for generating a distorted
multiple-input signal from the received multiple-input signal; and
a multiple-output for feeding the pre-distorted multiple-input
signal; wherein the pre-processing cells are configured so as to
estimate impairments generated by the multiple-input and
multiple-output transmitter and adjust the pre-distorted
multiple-input signal to compensate for the estimated
impairments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Embodiments of the invention will be described by way of
example only with reference to the accompanying drawings, in
which:
[0014] FIG. 1 is a block diagram of a Multiple Input Multiple
Output (MIMO) system with a pre-compensator;
[0015] FIG. 2 is a block diagram of an example of pre-distortion
linearization technique in the form of a cascade of a signal
processing block and a transmitter;
[0016] FIG. 3 is a graph of measured output spectrums of a Single
Input Single Output (SISO) transmitter with and without digital
pre-distortion linearization technique;
[0017] FIG. 4 is a block diagram of a dual branch MIMO
transmitter;
[0018] FIG. 5 is a block diagram of a MIMO system with a digital
pre-compensator having four cells and a dual branch MIMO
transmitter;
[0019] FIG. 6 is a graph of measured output spectrum of a dual
branch MIMO transmitter with and without the pre-compensation
signal processing technique and for the linear MIMO
transmitter;
[0020] FIG. 7 is a block diagram of a MIMO system with a number N
of RF paths cascaded with a digital pre-compensator;
[0021] FIG. 8 is a block diagram of a dual-band transmitter with
dual inputs and single branch nonlinear transmitter;
[0022] FIG. 9 is a graph of the output signal from a nonlinear
transmitter which shows intra-band and inter-band distortions;
[0023] FIG. 10 is a block diagram of a system comprising a
multi-cell processing pre-compensator cascaded with a dual-band
transmitter;
[0024] FIG. 11 is a block diagram of a system comprising a
multi-cell processing pre-compensator cascaded with a multi-carrier
transmitter; and
[0025] FIG. 12 is a diagram of a processing cells matrix for MIMO
systems.
DETAILED DESCRIPTION
[0026] Linear and nonlinear distortions are the main sources of
performance degradation in RF front-ends. These distortions affect
the signal quality and lead to an unacceptable data communication.
In situations where both linear and nonlinear distortions are
present simultaneously, the conventional signal processing
algorithms are not able to eliminate and compensate for these
distortions. To overcome this drawback, there is provided a signal
processing to simultaneously compensate for both linear and
nonlinear distortions and impairments.
[0027] Referring to FIG. 1, there is shown an example of a system
100, having multiple inputs 110 and multiple outputs 140,
comprising a Multiple Input Multiple Output (MIMO) RF front-end 130
having degraded performance due to the nonlinear behavior of the
integrated RF PAs and the coupling effects between the multiple RF
paths. In this case, the MIMO RF front-end 130 suffers from a joint
effect of linear and nonlinear distortions. A MIMO pre-compensator
processing block 120 is cascaded to the MIMO RF front-end 130 to
compensate for all linear and nonlinear distortions of the MIMO
system 100.
[0028] Referring now to FIG. 2, there is shown an example of
pre-distortion linearization 200 for a Single Input Single Output
(SISO) transmitter, which may be used to illustrate the basic
concept behind signal pre-processing methods. Pre-distortion
linearization 200 includes a signal processing block 220, which
pre-processes the input baseband signal 210 to generate a
pre-distorted baseband signal 230. Then the pre-distorted signal
230 is supplied to the nonlinear transmitter 240 to produce an
output signal 250. Both the signal processing block 220 and the
transmitter 240 have nonlinear behavior; however, the cascade of
both block 220 and transmitter 240 has a linear response.
Therefore, the output signal 250 is a linear amplified version of
the input baseband signal 210. If f(x) is a function that models
the nonlinear behavior of the transmitter 240 extracted using the
baseband input signal (z) 230, and the equivalent complex envelope
of sampled RF signal at the output of the transmitter (y) 250, the
pre-distortion function of the signal processing block 220, g(x),
has to satisfy the following set of relations:
y=f(z) and z=g(x)
f(g(x))=G.sub.ox Equation 1
[0029] where
[0030] G.sub.o is the linear or small-signal gain of the
transmitter 240.
[0031] FIG. 3 shows the output spectrum of the nonlinear
transmitter 240 presented in FIG. 2 with and without using the
signal processing block 220 (with linearization and without
linearization, respectively in FIG. 3). The use of the signal
processing block 220 significantly reduces the out-of-band
distortion of the signal and improves quality of the signal.
[0032] In transmitters for multi-branch MIMO systems, the
transmitter's linear and nonlinear distortions on each branch may
be coupled because of the interference and crosstalk between the
multiple front-ends of the transmitter. Indeed, crosstalk or
coupling is more likely to happen between the paths in the case of
multiple RF paths with the same operating frequency and power. This
crosstalk phenomenon is expected to be more significant in
integrated circuit (IC) design, where the size of the prototype is
a critical design parameter.
[0033] Referring to FIG. 4, there is shown a dual branch MIMO
transmitter 420 as an example of a multi-branch MIMO system 400.
The dual branch MIMO transmitter 420 comprises low pass filters
430A and 430B, up-converters 435A and 4358 and a local oscillator
(L.O.) 440, and nonlinear transmitters 445A and 445B. The
transmitters 445A and 445B exhibit nonlinear and/or linear
distortion behaviors. The distortion behaviors may include but not
limited to nonlinear power response of the active devices such as
the power amplifier, frequency response, memory effect, branch
imbalance, DC and carrier offset, and/or image interference.
[0034] The crosstalk or coupling in dual branch MIMO transmitter
may be classified as linear crosstalk, 455, and/or nonlinear
crosstalk, 450. The crosstalk is considered linear when the effect
of the crosstalk at the output of the transmitter 460 can be
modeled as a linear function of the interference 460B and desired
signal 460A. In other words, the input signals 410 affected by
linear crosstalk 455 do not pass through nonlinear components such
as 445A and 445B. Conversely, the nonlinear crosstalk 450 affects
the input signals 410 before it passes through nonlinear components
such as 445A and 445B. The nonlinear crosstalk produces undesired
signal 460C at the output of the dual branch MIMO transmitter 400.
The sources of nonlinear crosstalk 450 may be interferences in the
chipsets between the different paths of the MIMO transceiver and
leakage of RF signals through the common local oscillator 440
path.
[0035] Referring now to FIG. 5, there is shown a MIMO system 500
comprising a digital pre-compensator 520 with dual inputs and dual
outputs cascaded in front of a dual branch MIMO transmitter 540
similar to the one illustrated in FIG. 4 (with components 550A,
550B, 555, 560A and 5606 of FIG. 5 corresponding to components
435A, 435B, 440, 445A and 445B of FIG. 4). The digital
pre-compensator 520 uses a matrix of four processing cells 515 in
order to compensate for the dual branch nonlinearities and any
crosstalk and interference (impairments) between the two RF paths.
The digital pre-compensator 520 comprises means, for example the
processing cells, using the input signals 530 and output signals
570 of the dual branch MIMO transmitter 540 to estimate any
nonlinearities and interferences (impairments) and identify a
proper processing function for each of the four processing cells
515. After identification, the input signals 510 are supplied to
the four processing cells 515 to generate and adjust the
pre-distorted signals 530. Then the pre-distorted signals 530 are
supplied to the dual branch MIMO transmitter 540. The cascade of
the digital pre-compensator 520 and the dual branch MIMO
transmitter 540 exhibit linear behavior. The output signals 570 are
the linear amplified version of the input signals 510 without the
effect of the transmitter linear and nonlinear distortions and
crosstalk on the quality of the signals. Therefore, the digital
pre-compensator 520 compensate for all the linear and nonlinear
distortions and crosstalk (impairments) in the different branches
of the MIMO transmitter 540.
[0036] Referring to FIG. 6, there is shown the measured output
spectrum of the dual branch MIMO transmitter 540 for three cases:
case-1) in the presence of -20 dB crosstalk and without using the
digital pre-compensator 520, case-2) in the presence of -20 dB
crosstalk and using the digital pre-compensator 520, and case-3)
for a perfect MIMO transmitter without any crosstalk and
nonlinearities. The output spectrum of case-2 with -20 dB crosstalk
and digital pre-compensator 520 is almost following the one in
case-3; this demonstrates that the digital pre-compensator 520 can
compensate for the effect of both transmitter nonlinearities and
crosstalk (impairments).
[0037] Referring to FIG. 7, there is shown an example of a system
700 comprising a digital pre-compensator with multiple inputs and
multiple outputs 720, having a RF front-end 740 with a number N of
outputs 750. The digital pre-compensator 720 can be modeled as a
N.times.N matrix 725 where each cell of the matrix represents a
processing block. For example, D.sub.i,j represents the processing
block between the i.sup.th input signal and the j.sup.th output of
the digital compensator 720. The matrix representation of the
digital compensator block based on the input signals x 710 and
output signals Y 730 can be expressed as follows:
[ Y .fwdarw. 1 Y .fwdarw. i Y .fwdarw. N ] = [ A x .fwdarw. 1 A x
.fwdarw. i A x .fwdarw. N ] [ D 1 , 1 D 1 , 2 D 1 , N - 1 D 1 , N D
2 , 1 D 2 , 1 D 2 , N - 1 D 2 , N D N - 1 , 1 D N - 1 , 2 D N - 1 ,
N - 1 D N - 1 , N D N , 1 D N , 2 D N , N - 1 D N , N ] Equation 2
##EQU00001##
[0038] where the parameters in Equation 2 are defined as:
A x .fwdarw. = [ .beta. x .fwdarw. 0 .beta. x .fwdarw. q .beta. x
.fwdarw. Q ] is an N .times. K ( Q + 1 ) matrix , .beta. x .fwdarw.
q = [ 0 1 xq 0 1 xq 0 1 xq .beta. 1 ( x ( 1 ) ) .beta. 2 ( x ( 1 )
) .beta. K ( x ( 1 ) ) .beta. 1 ( x ( N - q ) ) .beta. K ( x ( N -
q ) ) ] is an N .times. K matrix , and .beta. k ( x ( n ) ) is
defined as : .beta. k ( x ( n ) ) = x ( n ) k - 1 x ( n ) Equation
3 ##EQU00002## [0039] and, x=[x(1) x(2) . . . x(N)].sup.T is an
N.times.1 vector representing N samples of the input signal, and K
and Q are the maximum polynomial order and memory depth.
[0040] Referring to FIG. 8, there is shown an example of a
multi-frequency MIMO system 800 in the form of a dual-band
transmitter 820 having inputs 810 and output 860. The dual-band
transmitter 820 consists of low pass filters 830A and 830B,
up-converters 835A and 835B, local oscillators (L.O.) 840A and
840B, and nonlinear transmitter 850. The input signals are
up-converted to carrier frequencies .omega..sub.1 and .omega..sub.2
from local oscillators 840A and 840B using up-converters 835A and
835B. The up-converted signals from the up-converters 835A and 835B
are combined by means of a power combiner 845 and are supplied,
after combination, to the dual-band transmitter 850. The dual-band
transmitter 850 exhibits nonlinear and/or linear distortions
(impairments) behaviors. The distortion behaviors may include but
not limited to nonlinear power response of the active devices such
as the power amplifier, frequency response and memory effect.
[0041] Referring to FIG. 9, there is shown the output signal of the
dual-band transmitter 820 presented in FIG. 8. Due to nonlinear
behavior of the dual-band transmitter 820, the output signal 900 of
the transmitter 820 consists of desired signals 910A and 910B at
carrier frequencies .omega..sub.1 and .omega..sub.2, intra-band
distortions 920, and inter-band distortions 930A and 9308.
[0042] Referring now to FIG. 10, there is shown a system 1000
comprising a digital multi-cell processing pre-compensator 1020
with dual inputs 1010 and dual pre-distorted outputs 1015 cascaded
in front of a dual-band transmitter 1030 similar to the one
illustrated in FIG. 8 (with components 1035A, 1035B, 1040A, 1040B,
1045A, 1045B, 1050 and 1060 of FIG. 10 corresponding to components
830A, 830B, 840A, 840B, 835A, 835B, 845 and 850 of FIG. 8). The
digital multi-cell pre-compensator 1020 uses a matrix of two
processing cells, 1025A and 1025B, in order to compensate for the
dual-band transmitter's nonlinearities and any intra-band
distortions (impairments) between the two RF signals. The digital
multi-cell pre-compensator 1020 with dual inputs 1010 and dual
outputs 1015 comprises means, for example the processing cells
1025A and 10258, using the input signals 1010 and output signal
1070 of the dual-band transmitter 1030 to estimate any
nonlinearities and distortions (impairments) and identify a proper
processing function for each of the two processing cells PC1 1025A
and PC2 1025B. After identification, the input signals 1010 are
supplied to the two processing cells 1025A and 1025B to generate
and adjust the pre-distorted signals 1015. Then the pre-distorted
signals 1015 are supplied to the dual-band transmitter 1030. The
cascade of the digital compensator 1020 and the dual-band
transmitter 1030 exhibits linear behavior. The output signal 1070
is the linear amplified version of the input signals 1010 without
the effect of the transmitter's nonlinearities and intra-band
distortions (impairments) on the quality of the output signal.
Therefore, the digital multi-cell processing pre-compensator block
1020 compensate for all the linear and nonlinear distortions
(impairments) of the dual-band transmitter 1030.
[0043] Referring to FIG. 11, there is shown a system 1100
comprising a digital multi-cell processing pre-compensator 1120
with dual inputs 1110 and pre-distorted output 1150 cascaded in
front of a multi-carrier transmitter 1160. The digital multi-cell
pre-compensator 1120 uses a matrix of four processing cells, 1125A,
1125B, 1130A and 1130B, in order to compensate for the
multi-carrier transmitter's 1160 nonlinearities and any intra-band
and inter-band distortions (impairments) between the two RF
signals. The digital multi-cell pre-compensator 1120 comprises
means, for example the processing cells 1125A, 1125B, 1130A and
1130B, using the input signals 1110 and the output signal 1170 of
the multi-carrier transmitter 1160 to estimate any nonlinearities
and distortions (impairments) and identify a proper processing
functions for each of the four processing cells PC1 1125A, PC2
11258, PC3 1130A, and PC4 11308. The processing cells PC1 1125A and
PC2 1125B compensate for the intra-band distortions and
transmitter's nonlinearities around carrier frequencies
.omega..sub.1 and .omega..sub.2. The processing cells PC3 1130A and
PC4 1130B compensate for the inter-band distortions at frequency
bands centered at 2.omega..sub.1-.omega..sub.2 and
2.omega..sub.2-.omega..sub.1. The pre-distorted output signals of
the processing blocks are then up-converted to designated carrier
frequencies using the up-converters 1135A, 1135B, 1135C, and 1135D.
Finally, the up-converted signals are combined in power combiner
1145 and feed the input of the nonlinear multi-carrier transmitter
1160. The cascade of the digital multi-cell pre-compensator 1120
and the dual-band transmitter 1160 exhibit linear behavior. The
output signal 1170 is the linear amplified version of the input
signals 1110 without the effect of the transmitter's
nonlinearities, inter-band, and intra-band distortions
(impairments) on the quality of the output signal. Therefore, the
digital multi-cell pre-compensator 1120 compensates for all the
linear and nonlinear distortions of the multi-carrier transmitter
1160.
[0044] Referring to FIG. 12, there is shown a system comprising a
digital pre-compensator 1220 with multiple inputs 1210 and multiple
outputs 1250 used for forward behavior modeling and simulation of
the linear/nonlinear behavior of multi-branches and
multi-frequencies MIMO systems. The digital pre-compensator 1200 is
modeled as a N.times.N matrix with N.sup.2 cells 1230, with N
inputs 1210 and N outputs 1250, where each cell of the matrix
represents a processing block. For example, D(i,j) represents the
processing block where the input of the processing cell is the
i.sup.th input 1210 of the MIMO system and the output of the
processing cell is the input of the function f.sub.j, which its
output is the j.sup.th output 1240 of the digital pre-compensator
1220. The functions f.sub.i 1240 can be modeled as linear or
nonlinear functions with/without considering the memory of the
system.
[0045] Depending on the architecture of the MIMO system, the
digital compensator with multiple inputs and multiple outputs 1220
can be added before or after the MIMO system as pre-compensator or
post-compensator.
[0046] Therefore, as taught by the above disclosure:
[0047] The pre-distorted multiple-input signal may be adjusted to
introduce linear and nonlinear distortions on each signal path of
the multiple-input signal to compensate for estimated impairments;
and
[0048] The pre-distorted multiple-input signal may be adjusted to
introduce interference between each signal path of the
multiple-input signal to compensate for estimated impairments.
[0049] Each of the above described pre-processing cells may include
nonlinear processing blocks compensating for multiple-input
multiple-output nonlinear distortions and an effect of
interferences between signal paths of the multiple-input signal and
signal paths of the multiple-output signal. The nonlinear
processing blocks process the multiple-input signal and the
multiple-output signal to determine a desired multiple-output
signal that pre-compensates for the nonlinear distortions; and
estimating a nonlinear function for each nonlinear processing
block.
[0050] Each of the above described pre-processing cells may include
linear processing blocks compensating for multiple-input
multiple-output linear distortions and an effect of interferences
between signal paths of the multiple-input signal and signal paths
of the multiple-output signal. The linear processing blocks process
the multiple-input signal and the multiple-output signal to
determine a desired multiple-output signal that pre-compensates for
the linear distortions, and estimate a linear function for each
linear processing block.
[0051] Each of the above described pre-processing cells of the
matrix may comprise nonlinear processing blocks compensating for
multiple-input multiple-output nonlinear distortions and an effect
of interferences between signal paths of the multiple-input signal
and signal paths of the multiple-output signal, and linear
processing blocks compensating for the multiple-input
multiple-output linear distortions and the effect of interferences
between the signal paths of the multiple-input signal and the
signal paths of the multiple-output signal. The non-linear and
linear processing blocks process the multiple-input signal and the
multiple-output signal to determine a desired multiple-output
signal that pre-compensates for the non-linear and linear
distortions, estimate a non-linear function for each non-linear
processing block, and estimate a linear function for each linear
processing block.
[0052] Each of the above described pre-processing cells of the
matrix may model a behavior of multi-input multi-output system and
may include a nonlinear processing block to compensate for the
multiple-input multiple-output system linear distortions and an
effect of interferences between signal paths of the multiple-input
signal and signal paths of the multiple-output signal, and a linear
processing block to compensate for the multiple-input
multiple-output system linear distortions and the effect of
interferences between the signal paths of the multiple-input signal
and the signal paths of the multiple-output signal. Each of the
non-linear and linear processing blocks process the multiple-input
signal and the multiple-output signal to determine a desired
multiple-output signal that pre-compensates for the non-linear and
linear distortions, estimate a non-linear model for each non-linear
processing block, and estimate a linear model for each linear
processing block.
[0053] Those of ordinary skill in the art will realize that the
description of the system and methods for digital compensation are
illustrative only and are not intended to be in any way limiting.
Other embodiments will readily suggest themselves to such skilled
persons having the benefit of this disclosure. Furthermore, the
disclosed systems can be customized to offer valuable solutions to
existing needs and problems of the power efficiency versus
linearity tradeoff encountered by designers of wireless
transmitters in different applications, such as satellite
communication applications and base and mobile stations
applications in wireless communication networks.
[0054] In the interest of clarity, not all of the routine features
of the implementations of signal pre-compensation processing
mechanism are shown and described. It will, of course, be
appreciated that in the development of any such actual
implementation of the network access mechanism, numerous
implementation-specific decisions must be made in order to achieve
the developer's specific goals, such as compliance with
application-, system-, network- and business-related constraints,
and that these specific goals will vary from one implementation to
another and from one developer to another. Moreover, it will be
appreciated that a development effort might be complex and
time-consuming, but would nevertheless be a routine undertaking of
engineering for those of ordinary skill in the field of
telecommunication networks having the benefit of this
disclosure.
[0055] In accordance with this disclosure, the components, process
steps, and/or data structures described herein may be implemented
using various types of operating systems, computing platforms,
network devices, computer programs, and/or general purpose
machines. In addition, those of ordinary skill in the art will
recognize that devices of a less general purpose nature, such as
hardwired devices, field programmable gate arrays (FPGAs),
application specific integrated circuits (ASICs), or the like, may
also be used. Where a method comprising a series of process steps
is implemented by a computer or a machine and those process steps
can be stored as a series of instructions readable by the machine,
they may be stored on a tangible medium.
[0056] Systems and modules described herein may comprise software,
firmware, hardware, or any combination(s) of software, firmware, or
hardware suitable for the purposes described herein. Software and
other modules may reside on servers, workstations, personal
computers, computerized tablets, PDAs, and other devices suitable
for the purposes described herein. Software and other modules may
be accessible via local memory, via a network, via a browser or
other application in an ASP context, or via other means suitable
for the purposes described herein. Data structures described herein
may comprise computer files, variables, programming arrays,
programming structures, or any electronic information storage
schemes or methods, or any combinations thereof, suitable for the
purposes described herein.
[0057] Although the present invention has been described
hereinabove by way of non-restrictive illustrative embodiments
thereof, these embodiments can be modified at will within the scope
of the appended claims without departing from the spirit and nature
of the present invention.
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